1. Field of the Invention
The present invention relates to an injector that is disposed in an internal combustion engine to inject fuel, which serves for combustion, through a nozzle hole.
2. Description of Related Art
In order to accurately control output torque and a state of emissions of an internal combustion engine, it is important to accurately control a state of fuel injection, such as injection start time and injection quantity of fuel injected from an injector. Accordingly, a technology for detecting an actual state of injection by detecting pressure of fuel that varies with the injection is conventionally proposed. For example, actual injection start time is detected by detecting the start time of decrease of fuel pressure in accordance with the injection start, and actual injection completion time is detected by detecting time for the stop of increase of fuel pressure in accordance with completion of the injection (see, for example, Japanese Unexamined Patent Application Publication No. 2008-144749 corresponding to US2008/0228374A1).
In detecting such a fluctuation of fuel pressure, the fluctuation of fuel pressure caused due to the injection is buffered in the common rail using a fuel pressure sensor (rail pressure sensor) that is disposed directly in a common rail (pressure accumulation container). Therefore, accurate fluctuation of fuel pressure cannot be detected. For this reason, the technology described in the Publication No. 2008-144749 aims to detect the fuel pressure fluctuation before the fuel pressure fluctuation due to the injection is buffered in a common rail, by disposing a fuel pressure sensor in an injector.
The above-described injector generically includes a body, a needle, and an actuator. The needle and actuator are accommodated in the body. The body has a high pressure passage, through which high pressure fuel flows into a nozzle hole, inside the body. The needle opens and closes the nozzle hole and the actuator drives the needle.
The present inventors have examined the attachment of a fuel pressure sensor configured in the following manner, to the above-described body. That is, the fuel pressure sensor is composed of a flexure element that is attached to the body and resiliently deformed upon application of fuel pressure to the element, and a sensor element that converts a value of flexure generated in the flexure element into an electrical signal and outputs the signal as a pressure detection value.
The present inventors have explored a metal-touch seal (metal-to-metal seal) by forming sealing surfaces on both the flexure element and the body and by pressing both the sealing surfaces against each other to closely-attach the surfaces so that high pressure fuel does not leak out of a joint surface between the body and the flexure element. Particularly, in a recent diesel engine, pressurization of fuel (e.g., about 200 MPa) is promoted. Thus, high-pressure fuel is easily and suitably sealed using the metal-touch seal as compared to a seal with a gasket between the body and the flexure element.
By closely-attaching the sealing surfaces to each other with the sealing surface of any one of the body and the flexure element plastically-deformed, sealing characteristics of the metal-touch seal are improved. However, the body needs to have higher hardness through carburizing treatment so as to hold out against stress concentration in the high pressure passage. Moreover, the flexure element needs to be formed to be thin-walled so that the element is resiliently deformed. Accordingly, a material having higher hardness needs to be selected to ensure strength that can resist high pressure fuel. In other words, both the body and the flexure element need to have higher hardness. Because of this, when the higher-hardness members are metal-touch sealed with each other, the above-described plastic deformation is insufficient and the sealing characteristics cannot be fully improved.